1. Field of the Invention
The present invention concerns a method of producing carboxylic acid and alcohol. More specifically, this invention concerns a method of producing carboxylic acid and alcohol by hydrolysis of a liquid, which contains a carboxylic acid ester, under the presence of an acid catalyst to obtain a reaction product liquid, comprised essentially of carboxylic acid, alcohol, water, and carboxylic acid ester, and distilling this reaction product liquid in a manner that is industrially advantageous.
2. Description of the Related Art
For the conventional production of polyvinyl alcohol, vinyl acetate is obtained by an acetoxylation reaction, in which ethylene and acetic acid are the raw materials; polymerizing this vinyl acetate to produce vinyl polyacetate; and performing an ester exchange reaction with methanol in the presence of a basic catalyst. The methyl acetate that is produced from the ester exchange reaction is hydrolyzed in the presence of an acid catalyst and recovered in the final stage as acetic acid and methanol, and the unreacted methyl acetate is circulated back and reused in the hydrolysis reaction.
A method of recovering methyl acetate as acetic acid and methanol is disclosed in p. 109 of xe2x80x9cPoval, xe2x80x9d edited by the Polymer Society of Japan (newly revised edition; Apr. 1, 1981). This method shall now be described with reference to FIG. 3. A saponification mother liquor, having methyl acetate and methanol as the principal components, is supplied from a saponification mother liquor feeding line 17 to an A distillation tower 18 and separated into a top distillate 19, having methylacetate and methanol as the principal component, and a bottom liquid 20, having methanol as the principal component. The top distillate 19 is fed into an extractive distillation tower 21 along with the return distillate from the top distillate 27 of a B distillation tower 26 (described below), and water is added to the tower top of extractive distillation tower 21 from extraction water feeding line 22 to perform extractive distillation.
The bottom liquid 23 of extractive distillation tower 21 has methanol as the principal component and is fed along with the abovementioned bottom liquid of A distillation tower 18 to a C distillation tower 37 and separated into a methanol distillate 38 and a bottom liquid 39, which contains sodium acetate, etc. Methanol distillate 38 is treated further as necessary and recovered as methanol. The top distillate of extractive distillation tower 21 is methyl acetate and water and is supplied from methyl acetate feeding line 24 to a hydrolysis reactor 25, filled with ion exchange resin or other acid catalyst, to obtain a reaction product liquid, which essentially contains acetic acid, methanol, water, and unreacted methyl acetate. This reaction product liquid is fed into B distillation tower 26 and separated into a top distillate 27, which contains methyl acetate and methanol, and a bottom liquid 28, which contains acetic acid and water. The top distillate 27 is the abovementioned return distillate, and this distillate is fed into extractive distillation tower 21. Hereinafter, the components of the mixture shall refer mainly to the principal components, and descriptions concerning minor components present only in small amounts may be omitted. The Figures are conceptual diagrams, and the reboiler, condenser, pump, and other accessory equipment that are normally used are all unillustrated.
The bottom liquid 28, which contains acetic acid and water, of B distillation tower 26 is fed to the tower top of extraction tower 29 and acetic acid esters, ketones, and other solvents are fed from the lower part of the extraction tower to extract acetic acid. 35 is the solvent feeding line, and 31 is the rundown line for the raffinate, which has water as the principal component. The extracted liquid 30 from the extraction tower top includes acetic acid, solvent, and water, and this extracted liquid is fed into azeotropic distillation tower 32, having the abovementioned solvents as the azeotrope former, and acetic acid is recovered from the lower part of this distillation tower. 36 is a recovery line for acetic acid. The top distillate of azeotropic distillation tower 32 is water and solvent, and this top distillate is separated by separator 33, and the solvents are circulated back from the abovementioned solvent feeding line 35 for use in the extraction tower, and the water is taken out via drain line 34.
However, the above-described conventional method has the following problems. Since the equilibrium constant of the hydrolysis reaction of methylacetate and water is small, being 0.14 at 50xc2x0 C. for example, and the temperature dependence thereof is also small. Thus when the hydrolysis reaction is carried out with a molar ratio of methyl acetate to water of 1, the degree of conversion of methyl acetate by hydrolysis will only be 27 mole % at the most. Since, as mentioned above, the temperature dependence of the equilibrium constant is very small, substantially improving the degree of conversion by hydrolysis is not possible even if the reaction temperature is increased. Although the degree of conversion by hydrolysis can be improved by increasing the molar ratio of water to methyl acetate, the acetic acid concentration of the bottom liquid of B distillation tower 26 will drop and the load placed on extraction tower 29 for concentrating the acetic acid will increase.
Thus, with the conventional method, an extraction tower is required for the acetic acid concentration process. In addition, not only is the load on the extraction tower increased when the molar ratio of water to methyl acetate is increased, but the azeotropic distillation tower 32 must also be operated with caution in order to prevent solvents and water from becoming mixed with acetic acid. An extremely large amount of labor is thus required for the operation of the conventional method. Although the above description relates to an example where methyl acetate is hydrolyzed, the same applies to other carboxylic acid esters.
A reactive distillation method to recover methyl acetate as acetic acid and methanol is disclosed in U.S. Pat. No. 5,770,770. With this method, hydrolysis is performed without taking methyl acetate out of the system, and the generated components can be separated by distillation at the same time. This method can thus be said to be a rational method. However, in order to increase the degree of conversion by hydrolysis by this method, the molar ratio of water must be large with respect to methyl acetate, and since the amount of energy required to produce acetic acid and methanol therefore becomes significantly large, the method is not industrially advantageous.
An object of the present invention is therefore to provide a method of producing alcohol and carboxylic acid from a carboxylic acid ester in an industrially advantageous manner by a simplified process that does not use solvents.
This and other objects have been achieved by the present invention, the first embodiment of which provides a method of producing carboxylic acid and alcohol, that includes:
hydrolysing a liquid in a hydrolysis reactor, said hydrolysis reactor including an acid catalyst, and said liquid including: (1) a carboxylic acid ester; and (2) at least a portion of a side stream taken from a first distillation tower operated in a total reflux condition, to obtain a reaction product liquid that includes a carboxylic acid, an alcohol, water and a carboxylic acid ester;
supplying said reaction product liquid to said first distillation tower and removing a first bottom liquid therefrom, said first bottom liquid including a carboxylic acid, an alcohol and water;
supplying said first bottom liquid to a second distillation tower and separating said first bottom liquid into a first top distillate that includes an alcohol, and a second bottom liquid that includes a carboxylic acid and water;
supplying said second bottom liquid to a third distillation tower and separating said second bottom liquid into a second top distillate that includes a carboxylic acid and water, and a third bottom liquid that includes a carboxylic acid;
circulating said second top distillate back to a tower top of said first distillation tower, and adding water to said tower top.
Another embodiment of the invention provides a method of producing carboxylic acid and alcohol, that includes:
supplying a liquid to a first distillation tower, said liquid including a carboxylic acid ester, and said first distillation tower being operated in a total reflux condition, to obtain a side stream;
supplying said side stream to a hydrolysis reactor that includes an acid catalyst to obtain a reaction product liquid that includes a carboxylic acid, an alcohol, water and a carboxylic acid ester;
supplying said reaction product liquid to said first distillation tower and removing a first bottom liquid therefrom, said first bottom liquid including a carboxylic acid, an alcohol and water;
supplying said first bottom liquid to a second distillation tower and separating said first bottom liquid into a first top distillate that includes an alcohol, and a second bottom liquid that includes a carboxylic acid and water;
supplying said second bottom liquid to a third distillation tower and separating said second bottom liquid into a second top distillate that includes a carboxylic acid and water, and a third bottom liquid that includes a carboxylic acid;
circulating said second top distillate back to a tower top of said first distillation tower, and adding water to said tower top.
With the present invention, since the reaction product liquid obtained by the hydrolysis reaction is fed into a first distillation tower, this distillation tower is operated in a total reflux condition. Accordingly, the carboxylic acid ester is not distilled-outside the system but rather is taken from the distillation tower as a side stream and fed to the hydrolysis reactor. The water of the amount consumed by hydrolysis is added to the tower top of the distillation tower to perform extractive distillation by water, and the concentration of the aqueous solution of carboxylic acid is not performed by the azeotropic distillation method. Carboxylic acid and alcohol can thus be produced in a stable manner from a carboxylic acid ester with an extremely simplified flow. In addition, with the present invention, since the amount of water used can be significantly reduced, the amount of waste water is significantly reduced.